๐Network Layer
-
transport segment from sending to receiving host
- sender: encapsulates segments into datagrams, passes to link layer
- receiver: delivers segments to transport layer protocol
-
network layer protocols in every Internet device: hosts, routers
Network Layer ํต์ฌ ๊ธฐ๋ฅ
Forwarding
HW; Data Plane ์์ญ
- move packets from a routerโs input link to appropriate router output link
Routing
SW; Control Plane ์์ญ
- determine route taken by packets from source to destination
Data Plane & Control Plane
- Data Plane : ํจํท ์ก์์ ๊ธฐ๋ฅ ๋ด๋น. (forwarding ๊ธฐ๋ฅ)
- local, per-router function
- determines how datagram arriving on router input port is forwarded to router output port
- Control Plane : ํจํท ๊ฒฝ๋ก ์ค์ , ๊ด๋ฆฌ ๋ฐ ์ ์ดํ๋ ๊ธฐ๋ฅ ๋ด๋น. (routing ๊ธฐ๋ฅ)
- network-wide logic
- determines how datagram is routed among routers along end-end path from source host to destination host
- 2๊ฐ์ง Control plane์ ๋ํ ์ ๊ทผ:
- ์ ํต์ ๋ผ์ฐํ
์๊ณ ๋ฆฌ์ฆ : ๋ผ์ฐํฐ ์์์ forwarding, routing ๋ชจ๋ ๋ค ํจ
- SDN(Software-defined network) : ์ค๋ฒํค๋๊ฐ ํฐ routing์ ๋ฐ๋ก ๋ถ๋ฆฌํ์ฌ remote-server์์ ๊ด๋ฆฌ
Per-router Control Plane
์์ ๋ฐฉ์
Individual routing algorithm components in each and every router interact in the control plane
![์
๋ก๋์ค..]()
Logically Centralized Control Plane
์ต๊ทผ ๋ฐฉ์
A remote controller computes, installs forwarding tables in routers by interacting with local control agents (CAs)
![์
๋ก๋์ค..]()
Network Layer Service Model
defines the characteristics of e2e transport of packets between sending & receiving hosts
๐Router
![์
๋ก๋์ค..]()
![์
๋ก๋์ค..]()
![์
๋ก๋์ค..]()
- Decentralized switching:
- Given datagram, using header field(dest. IP addr.) values, lookup output port using forwarding table in input port memory (โmatch plus actionโ)
- Goal: complete input port processing at โline speedโ
- Input port queuing: if datagrams arrive faster than forwarding rate into switch fabric (if the switch fabric is not fast enough, then input queueing delay or loss due to buffer overflow)
Destination-based Forwarding
Based only on destination IP address (traditional)
Generalized Forwarding
Based on any set of header field values
Switching Fabrics : Data Plane
![์
๋ก๋์ค..]()
- transfer packet from input buffer to appropriate output buffer
- switching rate: rate at which packets can be transfer from inputs to outputs
- N inputs: switching rate N times line rate (R) desirable
- often measured as multiple of input/output line rate (NR)
Switching via Memory
Switching via Bus
Switching via Interconnection (Crossbar)
Output Port
![์
๋ก๋์ค..]()
-
Buffering required when datagrams arrive from fabric faster than link transmission rate. Drop policy: which datagrams to drop if no free buffers?
- Datagrams can be lost due to congestion, lack of buffers
-
Scheduling discipline chooses among queued datagrams for transmission
- Priority scheduling โ who gets best performance, network neutrality
Output Port Queueing โ Buffering
Scheduling Mechanism
Priority
RR Scheduling
Weightened Fair Queuing (WFQ)