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Chapter 2 Network Categories & Devices Communication Networks Communication Networks Switched Networks Broadcast Networks Ethernet Circuit Packet Switched Switched PSTN Connection Oriented ATM WLAN Connectionless Internet Ethernet Dr. Atef Abdrabou 2 Switched Networks ⚫ A switched network consists...

Chapter 2 Network Categories & Devices Communication Networks Communication Networks Switched Networks Broadcast Networks Ethernet Circuit Packet Switched Switched PSTN Connection Oriented ATM WLAN Connectionless Internet Ethernet Dr. Atef Abdrabou 2 Switched Networks ⚫ A switched network consists of switching nodes and user devices connected by transmission links ⚫ Nodes not concerned with content of data ⚫ User devices could be computer, telephone,…etc ⚫ Node-User links usually dedicated point-to-point links ⚫ Node-Node links usually multiplexed links ⚫ Network is partially connected (redundant connection vital for reliability) Dr. Atef Abdrabou 3 Packet Switching (Section 18.2) ⚫ Data transmitted in small packets ⚫ ⚫ ⚫ ⚫ Data transfer method: Store-andForward transmission Network Performance ⚫ ⚫ ⚫ ⚫ B Node-to-node links shared Packets accepted while network is busy Prioritizing packets possible Data Transfer ⚫ ⚫ ⚫ Longer messages split into smaller packets Each packet contains a payload of user data plus a header for control info (e.g., addressing) Packets may not arrive in-order Packet overhead F Two Types ⚫ ⚫ Datagram Virtual Circuits Dr. Atef Abdrabou 4 Datagram vs Virtual Circuit (Section 18.2.1&18.2.2) Datagram ⚫ No call setup phase ⚫ ⚫ ⚫ Better if few packets More flexible ⚫ ⚫ Virtual Circuit ⚫ Routing can be used to avoid congested parts of the network Network can provide sequencing and error control Packets are forwarded more quickly ⚫ ⚫ More Reliable Less reliable ⚫ Dr. Atef Abdrabou No routing decisions to make Loss of a node looses all circuits through that node 5 Delay in Datagram-Switched Networks ⚫ ⚫ ⚫ ⚫ T is the packet transmission time = Packet Size/ Data Rate Waiting time w = queuing time + processing time in each switch Propagation time τ = Distance between two switches / Speed of light Example for the Total delay: 6 Dr. Atef Abdrabou Delay in Virtual-Circuit Switched Networks ⚫ Example: ⚫ Total Delay = 3T + 3τ + setup delay + teardown delay ⚫ ⚫ ⚫ Setup Delay = 2 * request/response message transmission delay Teardown Delay = teardown message delay No queuing time is assumed because the bandwidth is already reserved in the setup phase 7 Dr. Atef Abdrabou Example What is the total delay for a packet size 1500 Bytes that is being sent on a link with 2 datagram switches each having a queuing time of 200 µs and a processing time of 1 µs. The link length between two switches is 300 km and the data rate is 5 Mbps. The speed of light inside the link is 3 x 108 m/s. Suppose now the two switches work as virtual circuit switches. The setup request/response or teardown message delay size is 160 µs. Find the total delay. ⚫ Solution: (1) Datagram switching case: Packet Transmission time = 1500 * 8 / 5 M = 0.0024 s Packet Propagation time over a link= 300 x 103 / 3 x 108 = 1 ms Total delay = 3 * 0.0024 + 3 * 1ms + 2 * ( 200µ + 1µ) = 0.010602 s (2) Virtual circuit switching case: Total Delay = 3 * 0.0024 + 3 * 1m + 0.00048 = 0.01068 s 8 Network Categories 1- Wide Area Network ⚫ ⚫ ⚫ Provides long distance transmission of data over a large geographical area Point-to-point WAN ⚫ A point-to-point link like your home DSL connection to Etisalat Switched WAN ⚫ Usually connects end systems (such as LANs or servers) together using switches or routers Dr. Atef Abdrabou 9 2- Local Area Network (LAN) ⚫ ⚫ ⚫ Usually privately owned and links devices in an office, a building or a campus Covers small area (few kilometers) Common topologies are Bus and Star Dr. Atef Abdrabou 10 Typical LAN Structure ⚫ ⚫ ⚫ Section 13.1 Transmission Medium Network Interface Card (NIC) Unique MAC “physical” address Ethernet Processor RAM ROM RAM Dr. Atef Abdrabou 11 The IEEE 802 LAN Standards Section 13.1 In IEEE 802.1, Data Link Layer divided into: 1- Logical Link Control Sublayer 2- Medium Access Control Sublayer OSI IEEE 802 Network layer Network layer 802.2 Logical link control LLC Data link 802.3 MAC Physical layer 802.5 802.11 Ethernet Token Ring Wireless CSMA-CD LAN Various physical layers Other layer LANs Physical layer 12 Dr. Atef Abdrabou Encapsulation of MAC frames IP Packet LLC LLC PDU Header IP Data MAC Header FCS Dr. Atef Abdrabou 13 Logical Link Control Sublayer ⚫ ⚫ ⚫ IEEE 802.2: LLC enhances service provided by MAC It provides a means for exchanging frames between LANs that use different MAC protocols Offer the network layer a set of services while hiding the details of the underlying MAC protocol Dr. Atef Abdrabou 14 Medium Access Control Sublayer ⚫ ⚫ ⚫ ⚫ Coordinate access to medium Connectionless frame transfer service Machines identified by MAC/physical address Broadcast frames with MAC addresses Dr. Atef Abdrabou 15 IEEE 802.3 MAC Frame Section 13.2 802.3 MAC Frame 7 1 Preamble SD 6 Destination address Synch Start frame 0 6 Source 2 Length Information Pad 4 FCS address 64 - 1518 bytes Destination address single (unicast) address Single address group (multicast) address 1 Group address broadcast = 111...111 Source address first 24 bits assigned to manufacturer; next 24 bits assigned by manufacturer Cisco 00-00-0C Dr. Atef Abdrabou 3COM 02-60-8C 16 MAC Destination Address Types Section 13.2 ⚫ ⚫ ⚫ ⚫ ⚫ The least significant bit of the first byte defines the type of address If the bit is 0 (the second hexadecimal digit from the left is even), the address is unicast; otherwise, it is multicast The broadcast destination address is a special case of the multicast address in which all bits are 1s Example: Determine the type of the following MAC destination addresses: a. 4A:30:10:21:10:1A b.47:20:1B:2E:08:EE c. FF:FF:FF:FF:FF:FF Dr. Atef Abdrabou 17 Network Devices ❑ ❑ LAN Devices (Hubs and LAN Switches) Routers (for LANs and WANs) Dr. Atef Abdrabou 18 Ethernet Hubs & Switches Section 13.2 & 17.1 Single collision domain (a) ⚫ ⚫ ⚫ ⚫ ⚫ ⚫ (b) High-Speed backplane or interconnection fabric ⚫ ⚫ ⚫ ⚫ Twisted Pair Cheap Twisted Pair Cheap Easy to work with Bridging increases scalability Reliable Star-topology CSMA-CD Dr. Atef Abdrabou Separate collision domains Full duplex operation 19 Bridge (Switch) Function Section 13.2 Dr. Atef Abdrabou 20 Transparent Switches (Bridges) Section 17.1.2 ⚫ ⚫ ⚫ Interconnection of IEEE LANs with complete transparency Use table lookup, and ⚫ discard frame, if source & destination in same LAN ⚫ forward frame, if source & destination in different LAN ⚫ use flooding, if destination unknown Use backward learning to build table ⚫ observe source address of arriving LANs ⚫ handle topology changes by removing old entries Dr. Atef Abdrabou S1 S2 S3 LAN1 Bridge LAN2 S4 S6 S5 21 Transparent Bridge (LAN Switch) Design Aspects Section 17.1.2 ⚫ ⚫ ⚫ ⚫ ⚫ ⚫ ⚫ Connects similar or different LANs Identical physical / link layer protocols for similar LANs Bridging between similar LANs means no modification to frame content or format Can map between MAC formats for different LANs Minimal processing No encapsulation Bridging is transparent to stations 22 Dr. Atef Abdrabou Hubs, Bridges & Routers Section 13.2 & 17.1 ⚫ Interconnecting Hubs ⚫ ⚫ ⚫ Repeater: Signal regeneration ⚫ All traffic appears in both LANs Bridge: MAC address filtering ⚫ Local traffic stays in own LAN Routers: Internet routing ⚫ All traffic stays in own LAN Higher Scalability ? Hub Hub Two Twisted Two Twisted Pairs Pairs Station Station StationDr. Atef Abdrabou Station Station 23 Station Example: Routing Table for a host and Routers H1 H2 150.100.12.154 150.100.12.176 150.100.12.128 150.100.12.129 150.100.0.1 150.100.12.176 R1 To the rest of the Internet 150.100.12.4 H3 H4 150.100.12.24 150.100.12.55 150.100.12.0 Routing Table at R1 150.100.12.1 Destination Net Gateway Net I/F 127.0.0.1 127.0.0.1 Lo 150.100.12.0/25 150.100.12.4 Eth0 150.100.15.0/25 150.100.12.1 Eth0 R2 H5 150.100.15.54 150.100.15.11 150.100.15.0 150.100.12.128/25 150.100.12.129 Eth1 0.0.0.0.0 150.100.0.1 Ser0 42