Chapter 2: Point-to-Point Network

Question 1

What is Point-to-Point and how is it used?

Answer 1

• PtP connect customer LANs to provider WANs, and interconnect LANs
• LAN-WAN connection is a serial or leased line connection
• Leased lines given by carrier, always-on between 2 remote sites

Question 2

List 2 types of PtP and descrive them.

Answer 2

• Serial communication (bits transmitted sequentially over single channel)
• Parallel communication (bits transmitted simultaneously over multiple wires [think of etherchannel], sends a byte instead of bit, used typically for high bandwidth devices)

Question 3

What is the purpose of PtP?

Answer 3

• Used when a dedicated connection is required
• single, pre-established path
• path goes from customer premises, through provider, to remote customer premise
• connects 2 geographically dstant sites, typically more expensive than shared services
• always-on availability required for data sensitive traffic (VoIP, and video)

Question 4

What are the speeds of these serial bandwidth connections?
• DS0 (most fundamental)
• T1/E1
• T3/E3
• OC-1

Answer 4

• 64Kbps
• 1.54Mbps/2.04Mbps
• 34.36Mbps/44.73Mbps
• 51.84Mbps

Question 5

Describe WAN encapsulation?

Answer 5

• Data encapsulated into frames before going on WAN link for L2 protocols to use
• HDLC (default encap, dedicated link, circuit-switched)
• PPP (syc/async circuit, security mechanisms like PAP/CHAP)

Question 6

What is the difference between Regular and Cisco HDLC?

Answer 6

• Cisco HDLC can only work with other Cisco devices
• DATA packet is split into Protocol and Data field, protocol field makes it possible for single link to multiple network layer protocols

Question 7

What is PPP?

Answer 7

• connects to a non-cisco router
• encapsulates data frames to transmit over physical link
• ppp establishes direct connection over serial, phone line, trunk, cellular, radio or fiber
• has protocols like LCP and NCP
• has link quality control and supports PAP/CHAP authen
• require full-suplex circuit, with sync/async mode

Question 8

Describe LCP/NCP funtionality.

Answer 8

• LCP functions with data link layer, role in establishing,configuring, and testing connection
• establishes PtP link, as well as agree on encapsulation formats, auth, compression, and error detection
• NCP allows multiple network layer protocols, uses separate NCP for each (IPv4/IPv6 NCPs)
• NCP includes additional codes to indicate which network protocol is used (IPCP=8021/IPv6CP=8057)

Question 9

List PPP Frame structure points.

Answer 9

• Flag (single byte that indicates beginning/end of frame [0111 1110])
• Address (byte of [1111 1111] standard broadcast)
• Control (byte contains sequence [0000 0011], calls for transmission of user data in unsequenced frame)
• Protocol (2 bytes, iddentifies protocol being encapsulated)
• Data (0 or more bytes, contains datagram for the protocol specified)
• Frame Check Sequence (2 bytes)

Question 10

List PPP phases of a session.

Answer 10

• Link establishment and configuration negotiation (LCP)
• Authentication
• Network layer protocol configuration negotiation (NCP)
• Link maintenance in open state (LCP)

Question 11

What is LCP responsible for?

Answer 11

• Establishment
• Maintenance
• Termination

Question 12

What is NCP responsible for?

Answer 12

• Compression (negotiate the algorythm to compress TCP/IP frames to save bandwidth)
• IPv4 address (static or DHCP)