K 4 T325 Summary - etihadaouetihadaou.com/.../2015/12/T325-Summary-Session-10.pdf · T325 Summary Session 1 Block III ... means the GMM messages are carried over the intermediate

T325 Summary

Session 1

Block III – Part 2 – Section 2 - Continous

Network Architecture

Prepared by:

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Prepared by: Dr. Saatchi, Seyed Mohsen 2

Block III – Network Architecture

Q1: Different protocols are used for 2G, 2.5G and 3G Answer: True

Q2: 2G and 2.5G : different protocol stacks are used for the control plane and the user plane Answer: True

Q3: 3G : same protocols are used for the control place and the user plane Answer: True

Q4: What is the different between 2G, 2.5G and 3G in using the protocols. Answer:

2G and 2.5G : different protocol stacks are used for the control plane and the user plane

3G : same protocols are used for the control place and the user plane

Q5: Mention the protocols used in empty places for the layered protocols in 3G packet domain. Answer:

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Answer:

Q6: Each service provides data in blocks called data units

Answer: True

Q7: The set of blocks at each node is often known as the protocol stack Answer: True Q8: The set of blocks at each node is often known as the protocol stack, give an example: Answer:

• PHY protocol: UE and Node B • GPRS mobility management (GMM): UE and the SGSN

Q9: in previous figure The UE and SGSN are not adjacent on the diagram, which means the GMM messages are carried over the intermediate nodes (Node B and

RNC) by lower level protocols; in this case the radio resource control (RRC) and radio access network application protocol (RANAP). Answer: True Q10: In previous figure these transport the GMM messages but do not alter them in any way, so the intermediate nodes are invisible to the GMM protocol. Answer: True

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Q11: Each block can be thought of as communicating with the block of the same name at the other end point using the services of the layers below. Answer: True

Q12: Radio Link control (RLC) block in the RNC communicates with the RLC block in the UE, using the services of the medium access control (MAC) and PHY layers. Answer: True Q13: Blocks communicating in this way are said to be communicating on a peer-to-peer basis and the two blocks are often referred to as peer entities. Answer: True

Q14: Protocol interworking: A node converts from one protocol to another in each direction. Answer: True

Example: At the lowest level, the Node B has blocks labeled PHY and ATM

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Q15: Protocol interworking: A node converts from one protocol to another in each direction. Answer: True Q16: The blocks labeled PHY refer to the physical layer of the radio interface, which comprises a number of different physical channels Answer: True Q17: In 3G, the primary means of sharing the allocated radio bandwidth between

these channels is W-CDMA Answer: True Q18: What does the physical channels are used for: Answer:

User traffic

Transport of Signaling messages

Management of the radio link itself. Q19: PHY interworks at the Node B with the ATM protocol Answer: True Q10: ATM protocol is used to transport user traffic and Signaling messages across the fixed part of the network from the Node B to the SGSN (and the MSC for circuit-switched traffic) via the RNC Answer: True Q11: The RRC, RLC and Mac protocols to consider are those which are used to manage the flow of data between the UE and the radio access network and to

control the allocation of radio channels. Answer: True

• Note: The end points for all of these protocols are the UE and the RNC (except for one specific case which need not concern us here).

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Q12: This means that in virtually all cases the; Node B does not participate in these protocols it simply forwards the data to the UE Answer: True Q13: List some MAC Layer : Principal functions Answer:

• Prioritization between: • data flows addressed to a single piece of UE

• data flows addressed to different pieces of UE. • Multiplexing data units arriving from the upper layers onto the data

units delivered to the physical layer and demultiplexing flows in the opposite direction.

• Encryption (if this has not been carried out by the RLC layer) • Traffic volume measurement.

Q14: List some responsibility of RLC layer: Answer:

• Segmentation of data units received from the next layer up (the RRC layer) into smaller data units to be forwarded to the MAC layer.

• Reassembling data units received from the MAC layer into larger data units for forwarding to the RRC layer.

• If instructed to do so, the RLC layer will also routinely acknowledge packets and retransmit those which are reported by the receiver to contain errors.

Q15: List three types of communication channels (3G standards):

Answer: • Logical channels: data flows between the RLC blocks • Transport channels: the data flows between the MAC blocks • Physical channels: the data flows transmitted across the radio

interface by the physical layer Q16: The top layer of the three is the RRC protocol, which handles most of the major functions in the radio network, List those functions: Answer:

• Setting up of physical radio channels • Reporting of radio measurements • Transport of Signaling messages between the mobile and the core

network • It also instructs the RLC layer whether or not to acknowledge packets.

Q17: The three protocols (MAC/RLC/RRC) and the physical layer protocol PHY are classified together in the standards as the access stratum Answer: True

Note: The level which provides the UE with access to the core network

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Q18: Radio network controller needs to interact with the core network. Answer: True Q19: Radio network controller needs to interact with the core network, this will done by using a protocol called RANAP. Answer: True Q20: The RANAP, which is used to interact with the SGSN (and also the MSC in the circuit-switched domain).

Answer: True Q21: RANAP makes use of a version of the standard Signaling protocol used in the circuit-switched domain, Signaling System No. 7 (SS7). Answer: True Q22: The version of SS7 used in RANAP has been modified to run over ATM. Answer: True

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Q23: At the very top of the stack is the non-access stratum (NAS), which handles direct Signaling between the mobile and the core network. Answer: True

Q24: In the 3G packet domain, the principal constituent of the non-access stratum is the GMM protocol. Answer: True Q25: IP addressing in fixed networks is hierarchical Network/subnetwork address and Host address.

Answer: True Q26: IP addressing in fixed networks is hierarchical is used for routing purposes Answer: True Q27: List some problems of Mobility in IP-based Mobile networks in 3G Answer:

• If a device were to move from one subnetwork to another: • It could be come invisible at the subnetwork routing level,

since the top-level routing would direct the packets to the previous subnetwork.

• Since its IP address would almost certainly not match the addressing scheme of the new subnetwork, messages from the device might also be rejected by firewalls checking for valid source addresses.

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Q28: How to solve problem of Mobility in IP-based Mobile networks in 3G Answer:

• Solving the mobility problem for mobile data communication, therefore, depends on using the location information the network holds, in order to make the IP addressing system continue to work as the mobile moves from one subnetwork to another.

• A clever solution is for the network to put each IP packet inside another IP packet.

• The outer packet can then be used to get the message to the router to which

the mobile device is currently connected, at which point this router extracts the inner packet and sends it directly to the mobile device.

• This approach is known as tunneling, and in GPRS and 3G it is provided

using the GPRS tunneling protocol (GTP).

Q29: GTP stands for ________________________ Answer: GPRS tunneling protocol Q30: What will happen when an IP packet arrives at the GGSN from an external IP network addressed to an active mobile:

Answer: GGSN adds the GTP header and the UDP header and puts the result in an IP packet addressed to the radio network controller in whose area the mobile is located. GGSN sends the packet through the appropriate tunnel, which ends at the relevant RNC.

• The RNC then extracts the inner IP packet and forwards it to the user equipment using the RRC protocol and the lower layers in the access stratum.

The UE then handles the IP packet just as if it had received it from a local IP router.

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Q31: Packets from the UE to the GGSN follow a similar process and are routed by the GGSN to a specific external IP network depending on the session associated with the user traffic tunnel through which the packet arrived. Answer: True Q32: What does the inner and outer level represent: Answer:

• Inner level represents the packet to be sent through the tunnel • Outer level consists of the headers added by the tunnelling protocol.

Q33: GTP uses the user datagram protocol (UDP) to send the tunnelled packets and also adds its own control header, which is used, among other things, to identify which tunnel is which. Answer: True Q34: In GTP the session information in the packet-switched side of the network is

stored in a series of tables maintained by the SGSN and the GGSN called the packet data protocol (PDP) context. Answer: True Q35: In GTP structure each session is directed to a particular network physically connected to one GGSN, and this network is identified by a uniform resource locator (URL) known as the access point name (APN). Answer: True Q36: In GTP structure the APN and the tunnel identifiers are held as part of the PDP context tables. Answer: True Q37: Typical APNs point towards the internet via a network belonging to an internet service provider (ISP), or to a corporate data network. Answer: True

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Q38: In addition to data transfers to single recipients, 3G also offers a multicast streaming and download service called the multimedia broadcast and multicast service (MBMS). Answer: True Q39: MBMS stands for ___________________________ Answer: Multimedia broadcast and multicast service Q40: MBMS the Multimedia broadcast and multicast service allows an IP multicast

tree to be constructed within the mobile network, eliminating the need to send multiple copies of the data across the network. Answer: True Q41: Most networks offer additional facilities associated with the voice service, known as supplementary services. Answer: True Q42: List some of supplementary services: Answer:

• Call forwarding, call on hold, notification of a waiting incoming call, conference calls, prevention of calls to or from a mobile handset, voice mail

• 3G networks allow video calls • The user requests a video call using the normal phone number

and the network attempts to set it up with the called party.

• Second most popular service offered by mobile networks (after voice

calls) is texting, or SMS (short message service). Q43: In the circuit-switched domain, the Signaling required to set up and clear down calls uses the ISDN SS7 protocol, which can be seen as an early packet-based protocol. Answer: True Q44: Text messaging makes use of the SS7 protocol to deliver the messages, avoiding the need to reserve bandwidth to transmit a message. Answer: True Q45: Internet Access: the user is connected to the internet via an internet service provider working in partnership with the mobile network. Answer: True Q46: Access to corporate networks through a virtual private network (VPN): typically utilize an IPsec tunnel in order to provide an additional layer of security. Answer: True

• Note: IPsec is a set of protocols for making IP communication more secure.

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Q47: Multimedia Messaging Service (MMS): allows still pictures, video clips and audio messages to be sent, as well as much longer text messages than SMS permits. Answer: True Q48: Streaming services present audiovisual content to the mobile device for buffering and immediate replay Answer: True Q49: List two types of video streaming service:

Answer: • Mobile TV

• User can choose from a number of channels but is constrained by a programme schedule

• Content-on-demand. • Content is downloaded to the mobile device and can be

replayed several times • The content provider may restrict the number of times the

content can be played or specify an expiry date beyond which it is no longer available.

Q50: How data services are provided? Answer:

• The user is provided with a standard APN, which is a URL specific to the mobile network and which needs to be selected as a setting on a mobile device or on a USIM card associated with the device

• The APN points towards the GGSN interface connected to the ISP’s

network, and the mobile device can use this to set up web browsing sessions.

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Q50: How data (Multimedia Messaging) services are provided? Answer:

• Multimedia messaging is similar in one way to text messaging, in that it makes use of a multimedia messaging centre (MMSC) which is used to store and forward messages.

• Unlike the SMSC, however, the MMSC is a fully IP-based device which can only be accessed through an IP network.

• When the user wants to send a message, the user equipment sets up a session using an APN (URL) pointing to the MMSC.

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Q51: How an authentication will process function in 2G and 3G? Answer:

• In 2G, authentication is the process used to prove to the network that the mobile device is genuine and allowed to use the network.

• In 3G, the process is mutual; it also allows the mobile to prove to itself that the network is genuine.

• In both 2G and 3G, authentication is a function of the non-access stratum

• Takes place between the user equipment (actually the USIM card) and the core network without the intervention of the radio access network.

1. On receipt of an authentication request, the SGSN sends a request to the AuC to begin the authentication process.

2. The AuC does this by calculating an authentication vector (AV), which is a sequence of, which includes the following five components:

• RAND : a random number . • AUTN : the authentication token, which depends among other things

on a sequence number SQN, which the UE and the AuC synchronise between them, and the random number RAND .

• XRES : an expected result, to be used by the SGSN to check the authentication response from the UE .

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• CK : a temporary cipher key, to be used to encrypt the user data until the next authentication request .

• IK : a temporary integrity key, to be used to verify the integrity of Signaling messages to and from the UE.

3. SQN and RAND are used to prove that the AV has been freshly generated, to prevent replay attacks based on captured AVs.

Good Luck,,,

Documents

K 4 T325 Summary - etihadaouetihadaou.com/.../2015/12/T325-Summary-Session-10.pdf · T325 Summary Session 1 Block III ... means the GMM messages are carried over the intermediate